Medical Neuroscience explores the functional organization and neurophysiology of the human central nervous system, while providing a neurobiological framework for understanding human behavior. In this course, you will discover the organization of the neural systems in the brain and spinal cord that mediate sensation, motivate bodily action, and integrate sensorimotor signals with memory, emotion and related faculties of cognition. The overall goal of this course is to provide the foundation for understanding the impairments of sensation, action and cognition that accompany injury, disease or dysfunction in the central nervous system. The course will build upon knowledge acquired through prior studies of cell and molecular biology, general physiology and human anatomy, as we focus primarily on the central nervous system. This online course is designed to include all of the core concepts in neurophysiology and clinical neuroanatomy that would be presented in most first-year neuroscience courses in schools of medicine. However, there are some topics (e.g., biological psychiatry) and several learning experiences (e.g., hands-on brain dissection) that we provide in the corresponding course offered in the Duke University School of Medicine on campus that we are not attempting to reproduce in Medical Neuroscience online. Nevertheless, our aim is to faithfully present in scope and rigor a medical school caliber course experience. This course comprises six units of content organized into 12 weeks, with an additional week for a comprehensive final exam: - Unit 1 Neuroanatomy (weeks 1-2). This unit covers the surface anatomy of the human brain, its internal structure, and the overall organization of sensory and motor systems in the brainstem and spinal cord. - Unit 2 Neural signaling (weeks 3-4). This unit addresses the fundamental mechanisms of neuronal excitability, signal generation and propagation, synaptic transmission, post synaptic mechanisms of signal integration, and neural plasticity. - Unit 3 Sensory systems (weeks 5-7). Here, you will learn the overall organization and function of the sensory systems that contribute to our sense of self relative to the world around us: somatic sensory systems, proprioception, vision, audition, and balance senses. - Unit 4 Motor systems (weeks 8-9). In this unit, we will examine the organization and function of the brain and spinal mechanisms that govern bodily movement. - Unit 5 Brain Development (week 10). Next, we turn our attention to the neurobiological mechanisms for building the nervous system in embryonic development and in early postnatal life; we will also consider how the brain changes across the lifespan. - Unit 6 Cognition (weeks 11-12). The course concludes with a survey of the association systems of the cerebral hemispheres, with an emphasis on cortical networks that integrate perception, memory and emotion in organizing behavior and planning for the future; we will also consider brain systems for maintaining homeostasis and regulating brain state.
Brain Waves and Sleep Stages
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Medical Neuroscience
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Complex Brain Functions: Sleep, Emotion and Addiction
In this concluding module of Medical Neuroscience, we will consider the neurobiology of sleep and the neurobiology of emotion, including addiction. Both topics involve explorations of complex, widely distributed systems in the forebrain and brainstem that modulate states of body and brain.
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Leonard E. White, Ph.D.Associate Professor
Department of Neurology, Department of Neurobiology, Duke University School of Medicine; Department of Psychology & Neuroscience, Trinity College of Arts & Sciences; Director of Education, Duke Institute for Brain Sciences; Duke University
Well, okay, I think we're ready for a bit of a transition now to talk about stages
of sleep, and how they can be recognized clinically, and how they can be
monitored. So before I can describe in detail for
you the stages of sleep, we need to have a bit of a primer on
electroencephalography. Which is a means of recording this
ongoing activity of the human brain, which we sometimes call brain waves.
Well, I had opportunity to think about brain waves fairly recently, as I had a
very quick. vacation away from recording these videos
with you all and got to go to one of my favorite places on the planet and enjoy a
cool but beautiful day by the ocean watching waves and thinking about waves
in the brain. So I can't help but to watch waves on the
ocean. And think of waves of activity in the
brain and wonder how turbulent are the seas of electrical activity at the
moment, going on in, in my brain, perhaps yours as well.
And looking at the ocean is a just a. [NOISE] Intriguing reminder of the
rhythms in nature and those rhythms are present in the patterns of activity we
have in our brain. Sometimes we forget that, we consider
what's going on in our brain as being totally driven by what we're seeing or
what we're. Hearing or what we're saying but, in
reality, our brain is carrying out it's own rhythms, very much like these waves
before me. >> Well I always feel invigorated when
I visit that spot, and so with Some of those images in mind.
let's move on and talk about waves in the brain, and how we can measure them.
So the electrical activity in the cerebral cortex, of course, is ongoing.
And it reflects the integrated functions of, really tens of billions of neurons
across the cerebral hemispheres and this activity can generate macroscopic
currents that are flowing through the tissues.
And these electrical currents can be recorded from the scalp on the external
surface of the head. And this is the basis of this technology
called electroencephalography which is what we see here, so the scientists and
clinicians have standardized the numbers and placements of the electrodes on the
scalp that allow for systematic sampling of the cerebral mantle as it's present on
the superficial aspects of the brain. So what we're looking at here is the
placement of these electrodes as they are done in a standard experimental or
clinical environment. So, here's an illustration that attempts
to provide a bit of the principle involved here.
So, imagine that a neuron is receiving input from some source, and as these
neurons, receive that input. They're depolarized and ions are flowing
across the plasma membrane, and for excitatory post synaptic potentials, that
means positive charge is entering the post synaptic process.
So as that Positive charges entering the cell, that's essentially an inward
current. So that is a current sync.
There is a negativity at that site, where there is this, aggregate of active
synapses. So positive charge is going to flow
through the extracellular fluids. Towards that current sink.
So where that current is coming from then, is going to become the source of
current. And so, there are these sinks and
sources, these current dipoles that are in register [SOUND] throughout the
cortical mantle because of the organization of these pyramidal cells.
So wherever these pyramidal cells are oriented perpendicularly to the surface
of the skull we have the potential to be able to record these electrical dipoles
with a placement of an electrode close to the surface of the brain.
Now obviously as the, solsi of the cerebral mantle fold in upon itself its
going to be very difficult to record dipoles that are buried in the depth of
the sulkus. So electroencephalography really is
limited to these more superficial dipoles that are present on the crests of the
gyri of the cerebral hemispheres. [SOUND].
Well, what we actually record, then, reflects the aggregate activity of these
neurons. And so, at any one location, we're going
to have. The active inputs that are engaged in
some kind of pattern of neural activity. Whether we actually see that at the
surface of the scalp is going to depend upon a variety of factors, mainly the
number of active neurons that underlie the scalp electrode.
The firing rate of those active neurons and most importantly the synchrony of the
active population. So here for example we see a a cluster of
neurons receiving inputs, and when these inputs are firing in an, in a regular
fashion we find that each one neuron might be generating electrical signals
that when attenuated in time have the form of these various waves, and the
algebraic sum of those waves, which is what would be seen with the scalp
electrode, is a low-amplitude but higher frequency kind of pattern.
So this is consistent with an irregular pattern of activity at the level of
inputs to a population of neurons. This is actually consistent with the
transfer of information and the processing of signals that might be going
on within a cortical column. Now, on the other hand, if it were
possible to synchronize the inputs to this population of cells, we may find
that many neurons are essentially engaged in firing at more or less the same time.
And these signals might then sum algebraically and produce a much more
noticeable wave in the electroencephalographic recording from
the surface. So when there is synchronous input
activity to a local region of the cerebral cortex, we tend to have higher
amplitude. But lower frequency oscillations that can
be recorded. And as we'll see the synchronized pattern
of activity is indicative of non-rem sleep.
Well there is another context in which one can see highly synchronous activity
and it's not good. Highly synchronous
electroencephalographic activity can be the hallmark of a seizure.
So, this is a representation of electroencephalographic data from an
individual that, experienced a seizure. So here we see a healthy looking.
high frequency, low amplitude activity recorded between pairs of scalp
electrodes. And then with the onset of the seizure,
we see this massive synchronous discharge, as indicated by these high
amplitude, lower frequency waves That emerge in this patient, synchronously,
across the entire brain. So this would be an example of what we
call a generalized seizure, because it involves almost the entire brain all at
once. So this pattern of brain activity would
be considered to be pathological. So, putting that aside for the moment.
Normal patterns of electroencephalographic activity
generally fall into four recognized frequency bands.
beginning with the lowest frequency bands we can see healthy brain oscillating.
And very large amplitude, very slow waves in what's called the Delta band, this is
one to four cycles per second, one to four hertz.
This as we'll see is indicative of the deepest stage of sleep.
The next highest band of activity that is recognized is called the theta band and
this is a rhythm between 4 and 7 hertz. Theta activity is consistent with being
awake and perhaps being engaged in some sort of active exploration of your
surroundings. Next we have the alpha band, the alpha
rhythms. Alpha is between 8 and about 13 hertz.
And the alpha rhythms seem to be a prominent feature of our sensory cortical
areas, especially when those cortical areas are.
Somewhat disengaged from the sensory environment.
So, if for example, if one were to close ones eyes.
You'd find that the visual cortex very quickly will go into a alpha rhythm.
With large amplitude waves in this eight to 13 or so hertz range.
And when we open our eyes for most people anyway the alpha rhythm will go away just
about immediately, so the alpha rhyme is an indication that a sensory cortex is in
a state of quiet rest. Now the highest frequency waves that we
typically recognize are in the, beta range sometimes we split this into beta
and gamma with, beta being anything above 12 hertz basically.
And gamma being around 40 to 60 hertz. So gamma waves beta waves these are high
frequency but very low amplitude waves. So this would be indicative of a high
degree of. irregular activity or high degree of
desynchronization within cortical networks, and this might be consistent
with the [UNKNOWN] granular processing of information that is happening at the
Culumnar or perhaps the modular level... within our cortical networks.
So electroencephalographic recording is very important from a clinical
perspective. It can be used to diagnose disorders like
epilepsy or seizure disorder and it can be used to investigate various stages of
consciousness, including the normal transitions from sleep to wakefulness and
then back to sleep again. As well as, brain states that are
associated with injury to the brain itself.
Including coma and minimally conscious states of activity.
So let's now see how electroencephalographic data can be used
to categorize the various stages of sleep.
Well, the electroencephalogram has provided psychiatrists and other kinds of
physicians who study sleep the opportunity to characterize the
progression of an individual from being fully awake to being deeply asleep, and
we use these electroencephalogramic criteria to recognize essentially.
Five stages of sleep. Four stages of non-REM sleep, and then we
can recognize REM sleep, based on the behavior of the individual and the
electroencephalographic record. So stage one sleep is a time when we are
beginning to feel drowsy. we are otherwise still awake but
beginning to experience that transition from being vigilant to being quite
drowsy. So during stage one sleep, we begin to
see the emergence of some higher amplitude rhythms.
Still fairly fast and the increase in amplitude only modest, but it's
consistent with The increase in synchronicity that is going to lead to
more deeper stages of sleep. So, in stage two sleep, then, this is the
next deeper stage. We see an increase in amplitude.
And then we see the emergence of a very particular feature that is characteristic
of this stage of sleep. It's called the sleep spindle.
And this sleep spindle is a very brief, just a few seconds of high-frequency
activity that occurs in these clusters. So it's a high-amplitude, high-frequency
burst that is indicative of There being a great deal of synchrony imposed upon
thalamocortical neurons but only for these little brief epochs of time.
And so this is something that's happening as we begin to enter our deeper stages of
sleep. So stage two sleep might pass after 15 or
20 minutes or so and we begin to get into a stage of sleep that, more clearly is
increasing the amplitude of some of these brain waves.
So the electroencephalogram evidence is suggesting that the brain is, getting
even more hypo synchronous but that the rhythms are also slowing.
So with stage three sleep we're getting into fairly moderate levels of sleep.
The sleep spindles have gone away now and the electroencephalogram is characterized
by the emergence of these larger amplitude waves, but we see the deepest
stage of sleep. In state four, and this is when the
electroencephalogram reveals large amplitudes, slow delta waves, and these
waves are indicative of a cerebral cortex that is dissociated from its environment
and is engaged in this hyper synchronism slow rhythm of thalamocortical
oscillation. Now, once we cycle down to stage 4, to
deep sleep, after some period of time, maybe an hour, an hour and a half or so,
something fairly dramatic happens. We begin to step out of that deep slow
wave sleep, and we enter a stage of sleep Where the electroencephalogram reverts to
a low-amplitude, high-frequency pattern, something that resembles actually what
the electroencephalogram looks like in the awake state.
This is called REM sleep. REM stands for rapid eye movement sleep.
It's also called paradoxical sleep. And the paradox is, how can we be still
asleep and yet have electroencephalographic activity that
resembles an awake brain.
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